The present invention relates to an optical apparatus for a fingerprint recognition system, and more particularly, to an optical apparatus for a fingerprint recognition system which uses the characteristics of a beam emitted from a light source with respect to the absorption at ridges and reflection at valleys of fingerprint of individual finger laid on a surface of triangular prism.
As shown in FIGS. 1 and 2 which show an embodiment of a known optical apparatus for a fingerprint recognition system, the known optical apparatus comprises an LED (light emitting diode) array 20 as a light source for emitting light, a diffuser 3 for scattering the emitted beam from the LED array 20, a triangular prism 4 providing a slant surface for laying a subject finger, an image producing lens system 30 for producing a fingerprint image by receiving the reflected beam from the triangular prism 4, an area CCD (area charge coupled device) 6 for converting the produced fingerprint image into an electric signal, and an amplifying/analyzing circuit 19 for amplifying and then analyzing the electric signal converted at the area CCD 6 upon receiving it therefrom.
The operation of the above-mentioned known optical apparatus starts the fingerprint recognizing operation thereof as emitting a beam from the LED array 20 to the diffuser 3 wherein the beam is scattered, upon laying a subject finger on the slant surface of the triangular prism 4. In the prism 4, the scattered incident beam from the diffuser 3 is absorbed at ridges, contacting to the slant surface of the prism 4, but reflected at valleys, not contacting to the slant surface, of the fingerprint, then the reflected beam is reflected to the lens system 30 which processes the reflected beam which produces the subject fingerprint image upon the area CCD 6. The area CCD 6 converts the produced image into an electric signal and outputs the signal to the amplifying/analyzing circuit 19 wherein the signal is amplified and analyzed in order to recognize the subject fingerprint.
However, in the known optical apparatus, the object being processed, that is to say, the subject finger is laid as oriented at a non-normal angle to the path of the beam of the image producing lens system 30 so that the produced fingerprint image upon the area CCD 6 may be also oriented at a non-normal angle to the path of the beam, thereby causing the produced fingerprint image to be distinct near the path of the beam but gradually indistinct in proportion to the distance from the path of the beam. Such a phenomenon encountered in the orientation of the object at a non-normal angle to the path of the beam in the known apparatus may produce erroneous results in the fingerprint recognition. Other problems occur when the image producing lens system 30 comprises several lenses overlapping with one another in order to solve the above-described drawback. The optical apparatus having the image producing lens system comprising several lens has other problems that it introduces such as the expense and size thereof.